Abstract: Cilia have diverse roles in motility, sensory reception and signaling, and defects in cilia function contribute to human diseases such as polycystic kidney disease (PKD) and Bardet Biedl Syndome (BBS). Functionally coordinated intraflagellar transport (IFT) motors assemble and maintain cilia by transporting ciliary precursors, bound to protein complexes called IFT particles, from the base of the cilium to their site of assembly at the distal tip.We are studying the IFT motors that build sensory cilia on the dendritic endings of chemosensory neurons of the model organism Caenorhabditis elegans. Using a time-lapse fluorescence microscopy assay to observe IFT in wild-type and ciliary mutant animals, we observed that two kinesin-2 motors, heterotrimeric kinesin-ll and homodimeric OSM-3 kinesin, function as anterograde IFT motors, whereas IFT dynein drives retrograde IFT.The work proposed here is aimed at illuminating the mechanisms of IFT in this system. The specific aimsare: -1. To use in vivo transport assays and in vitro motility assays to probe the mechanisms by which functionally coordinated kinesin-ll and OSM-3 motors cooperate to move an IFT-particle along the cilium. - 2. To use ciliary mutants and transport assays to dissect mechanisms of IFT in sensory cilia by; a. analyzing a putative OSM-3 docking-activation complex; b. identifying molecules driving the delivery of the IFT machinery to the base of the cilium and regulating the reorganization of IFT components and motor switching at ciliary turnaround zones; and c. identifying the cargo molecules that the IFT machinery delivers to the sensory ciliary axoneme, membrane or matrix. In addressing these specific aims we hope to learn how IFT motors are coordinated and controlled, what specific cargoes are transported along cilia by the IFT machinery, how components of the IFT machinery are transported through the cytoplasm, and how defects in IFT may contribute to ciliary dysfunction and disease.